Case IH 3964 (DTC 125D) - ECU – Engine Control Unit (ECU): ECU temperature sensor 2 is too high

The control module has detected that the temperature reading from its secondary internal temperature sensor has exceeded the maximum allowable threshold. This condition typically points to the module physically overheating or a failure of the internal thermistor itself.

• MAXXUM T4E
• Case IH 240 Series Axial-Flow® Combines
• Case IH A8000 Sugar Cane Harvesters
• Case IH A8800 Sugar Cane Harvesters

1. 1

   Inspect the physical mounting location of the Engine ECU for accumulated debris, dirt, or chaff that could act as an insulator and prevent heat dissipation.

2. 2

   Verify that all factory heat shields between the engine/exhaust components and the ECU are intact and properly secured.

3. 3

   Connect the Case IH EST and monitor live data for 'ECU Temperature Sensor 2'. If temperature reads excessively high on a completely cold machine, the internal sensor has failed. If it rises gradually during operation, the ECU is genuinely overheating.

4. 4

   Check the ECU harness for short circuits. A short in an external actuator circuit powered by the ECU can cause internal drivers to overheat.

1. 1

   Clean the ECU Housing

   Thoroughly blow off the engine compartment and the ECU housing with compressed air to ensure cooling airflow is restored.

2. 2

   Clear and Retest

   Clear the inactive fault codes using the EST or the machine's diagnostic display. Run the engine under load to see if the code returns.

3. 3

   Address External Heat Sources

   If the ECU is getting too hot due to a missing heat shield or a rerouted exhaust leak, replace the shield or fix the exhaust leak.

4. 4

   Replace the ECU

   If the diagnostic checks prove the sensor is reading falsely (e.g., reading 115°C+ on a cold engine), the entire Engine ECU must be replaced as the internal sensor cannot be serviced individually.

5. 5

   Reprogramming

   If the ECU is replaced, the new module must be flashed with the correct machine software and engine calibration files using the Case IH EST.